Sympathetic ink



Patented June 8, 1937 UNITED STATES PATENT OFFICE No Drawing. Application August 29, 1934, Serial No. 741.930 a 15 Claims.

My invention relates to an improved sympathetic ink and method of making and using the same.

Sympathetic inks may, for purposes of description, be considered as falling into three general groups, namely, those in which the writing is made evident by the application of heat, those in which the writing is brought out by the use of chemicals wherein a chemical reaction takes place, and, finally, sympathetic inks of a class which become visible when the paper or other medium on which they are'applied is immersed in water or otherwise wetted. It is to the latter class of inks that my present invention relates.

5 Inks which become visible when the paper is wetted have been made heretofore. Such inks, however, have been incapable of fully successful use as printing inks, particularly for continued use on modern high speed presses. Many difierent types of difficulties are involved, most of which are well-known to those skilled in the art.

The principal object of. my present invention is the provision of an improved sympathetic ink.

Another object is the provision of a sympathetic ink which, when applied to paper and the r paper afterward wetted, will show the outline of the characters applied with the ink.

Another object is the provision of an ink of this character, wherein the characters will remain visible even though the paper may be soaked in water for a considerable period of time.

Another object is the provision of such an ink which will continue to appear and disappear even though the paper on which it is applied may be 35 repeatedly wetted and dried.

Another object is the use of a sympathetic ink of the character identified for use on either sized or unsized paper.

Other objects and features of my invention will 40 be apparent from the following detailed descrip tion.

I shall first describe the ink of my invention as it is produced for use on unsized paper stock, such as ordinary news print, for example. For

45 printing on this type of paper, an ink is produced which, in effect, applies a moisture resistant material having the character of a size to the portion of the paper covered by the ink, the moisture resistant material or solute material being made 50 to penetrate the fibers of the paper and to be entirely invisible when the paper is dry. When the paper is immersed in water, however, the portion of the paper not covered with sympathetic ink is readily wetted; while the portion of the 55 paper covered by the sympathetic ink is not readily wetted and the design of brought outplalnly.

According to the preferred form of the invention, the ink consists of a material not readily wetted by water such as cellulose nitrate and a solvent having a vapor pressure range between 0.1 and 10 millimeters of mercury at 20 C. The concentration of the solute moisture resistant material in general should range from /i.% to 5%, depending 'upon the material and the conditions surrounding its use. The final ink is a colorless mobile liquid having the property of making the paper more resistant to wetting by water in the manner described, but being of such a nature .that after it has been applied to the paper and the solvent evaporated, it leaves no mark upon the paper which can be detected by the unaided eye.

A very suitable ink made in accordance with the invention and with which I have obtained unusually good results consists of one part by weight of cellulose nitrate and ninety parts by weight of Cellosolve acetate (ethyl ether of the monoacetate of ethyleneglycolthe inkis In place of the Cellosolve acetate, I may employ other solvents having a relatively low vapor pressure within the range indicated. Examples of such solvents are amyl alcohol; normal butyl alcohol, di-acetone alcohol, ethyl Cellosolve (mono-ethyl ether of ethylene glycol), ethyl Cellosolve acetate, methyl Cellosolve, butyl Cellosolve, Carbitol" (mono ethyl ether of diethylene glycol), butyl lactate, and di-gnethyl phthalate. I may also use such solvents as the mixture of relatively higher boiling point solvents sold by the Du Pont Company under the trade name of H. T. P. 23, which has a vapor pressure at 20 C. of about 1.3 millimeters of mercury, and which comprises a mixture of high aliphatic alcohols and ketones from about C4 to Ca. I

Instead of cellulose nitrate, I may also employ other solute materials including other cellulose derivatives such as cellulose acetate. Certain synthetic and/or natural gums and resins can also be used such as pontianac,kauri,, gum ester, ordinary rosin, etc. I may also use certain metallic soaps, such as aluminum palmitate, as well as water insoluble plasticizers, using the term plasticizer in the sense in which it is used in the varnish, lacquer, and/or paint industries. Examples are the chlorinated diphenyls, diphenyl ethers, the condensation products of f rmaldehyde and thiourea, and the like.

All of the materials which I have employed successfully as solute materials are non-volatile, colorless, water insoluble, organic substances, having little or no gloss when applied in. proper proportions to paper, and are capable of being deposited within the'fibers of the paper in a definite, controllable outline. Some modifications .in

proportions of solvent may be necessary in order to insure deposition of the proper amount in the paper so that whensuch paper is afterwards.

, wetted, the pattern formed by the sympathetic ink will become visible; and also so that when.

, solute material is employed. For example, equal the paper is again thoroughly dried, theunaided eye will not be able to detect the-presence of' the invisible writing. In general, however, the total amount of solute sizing material in-the ink should compriseat leastone-quarter of one percent of the ink-and should not comprise more than about fi'vepercent of the ink, the remaining portion of the ink consisting of the low vapor pressure solventmaterial. F orgeneral use,about,pne percent of soluteleads .to the best result.

. v For operating on sometypes of paper andunder certain conditions, improved results are obtained if a mixture of more than one type of proportions. of cellulose xnitrateuand. rosin dissolved in a suitable proportion ofv Cellosolve acetate can be used'with good results. I I ,1

From the foregoing description, it is plain that ofmy improved ink hasthe effect of applying to the paper a material or substance which will affectthe water permeabilityof the paper..

when the inventipnis applied topaper having little ornosize. my eflect is obtainedpreferably by the useof an ink which will resist penetration of the water or, in other words, repel or resist wetting by, the water while the balance .of the paper is quickly permeated or saturated. In-

dependent-of the character of the solute material employed, I have found that securing of proper results, particularly .whengthe ink is used on modern printing" presses, is dependent to a great iextent upon the use of a solvent having certain characteristics which I have discovered are essential."

.I have found, that if the" solvent employed has a vapor pressurenotgreater than 7.5 millimeters of-mercury at 20 C., the ink canbe made to feed properly on ordinary highspeed presses. Unless the solvent has a vapor pressure at least this low, itwill evaporate onthe rolls, thereby causing the ink to thicken and resulting in the deposit of "large anamount of solute on the paper. This results in the ink becoming faintly visible andtherefore is objectionable forits intended purpose. With certain types of solute materials,

such as .cellulose. nitrate or rosin, the. ink also becomes sticky or tacky if the solvent, has a vapor pressure in excesspf 7.5 millimeters of mercury at 20 C. due to evaporation of the'solvent and thickening of the ink. Under extreme conditions, this may cause atearing of the inkin'g rolls and also follows .thetype.

, I have also found thatsuitable resuits'srenet obtained unless the solvent has a vapor pressure 1 at least' as great as 0.1 millimeter of mercury at 20C. If the solvent has a lower vapor pressure than that given, it will have a tendency to evapcrate too slowly, or even. may remain in the paper I almost indefinitely. It is important; for proper operation that the solvent be substantiallvall evaporated before the paper is stwked as it is droscopicity.

-. will be expected to in the ink ofmy invention. I. have found. howvapor pressure of four b61118 Printed. I have found that a solvent having a vapor pressure of not less than 0.1 millias water under comparable conditions in order "io'rztherelatlvely small amount of solventrapv plied to the paper to penetrate the fibersthereof and carry the solute material with it before it evaporates. The solvent employed must also be compatible with water to such an extent that a relatively slight amount of moisture on the will not repel its penetrating action. Ifthe ink is not compatible with moisture in relatively 1 small. amounts, diii'erent results: be obtained during different weather conditions. Assn example, commercial naphthas may. the obtained having a vapor pressure. of about' four'millime'ters of mercury .at 20- be suitable solvents for-use ever, that these naphthas seem to be repelled by only ,very slight amounts of moisture 'which are found on thesurface of the paper on a, damp C.,.Whlch in manyrespects day. .I havefound also that the surface tension 4 v of these naphthas isnot sumciently low to cause .a penetration of the fibers of the paper. Other examples of solvents unsuited for usein mylnvention could be given, but it is not believedlthat fiu'ther examples will add to the disclosure.

The useof a solvent having the characteristics of relatively very low vapor pressure; relatively low surface tension, andcompatibility with 'slight traces of moisture, all co-operateto cause a quick penetration of thefibersof the paper. thus avoiding the deposit of the solute material on .the very outside surface of the paper and at theqsame time reducing the tendency to form a gloss whichicould be detected by the'unaided eye when the paper was ina dry'state. -By establishing a lower limit of vapor pressure, sufficiently rapid evaporation is obtained. The resultis that during the relatively short space of time between printing and stacking, the. ink is caused to penetrate the paper and the solvent at the-same time is given an opportunity toevaporate.

' While I have given a vapor pressure range between 0'.1 millimeter of mercury at20 C. and 7.5 millimeters of mercury at 20C., it is tube understood that this represents azworkable range which I have determined by numerous experiments. I

prefer, however, to employ a solvent having a vapor pressureof approximately one millimeter.

of mercury or to establish a closer range, between .5 and 1.5 millimeters. I have found that. a sympathetic Iink employing a solvent within this range is capable of general asolvent havinga higher or'lower vapor pressure than about one millimeter of mercury may a be limitedinits application- I v For example, Ihave produced an ink employing i solvent having a with full satisfaction, howev on a Miehle type ofpress. An ink employing "'Cellosolve" acetate (vaporpressure 1.26 millimeters of mercury at millimeters of mercuryat. 20? C. whichis satisfactory for presses such as. ,a Gordon press; The sameink cannot be used i use on substantially all types ofpress equipment. An ink employing ion such as sodium.

20 C.) is very satisfactory on a Miehle type of press, but can also be used on a Gordon press. Indeed, I have found that this particular solvent can be used successfully in an ink intended for use on any type of press with which I am familiar.

The inks described above are liquid and are best employed by the use of a fountain arrangement such as that described in my co-pending application Serial No. 741,929, filed August 29, 1934. I may, however. compound such inks so that they will have approximately the same consistency as standard printing inks. By the use of a relatively small amount of a water insoluble soap, the ink can be produced in the form of a gel having the consistency desired. The proportion of soap used varies with the amount and character of both the solute material and solvent, and also depends upon the consistency of the gel desired. In general, I do not prefer the use of this character of ink, however, on unsized paper, because of the dimculty of securing adequate penetration into the fibers of the paper. An ink of this kind may be readily made which may be thoroughly satisfactory on one type of paper but as soon as the paper is changed, a trace of the ink markings may be visible when the paper is dry. It should be noted that I may employ certain metallic'soaps alone as the solute material, in which case a liquid ink may be produced.

When printing on bond paper or similar sized paper, the ink may be modified. if desired, by causing the portion of the paper covered with the ink to become more permeable to moisture instead of rendering it less permeable. When using bond paper, it is not so necessary to cause a deep penetration of the fibers'as is the case when an unsized paper is used. I find that suitable results may be obtained on bond paper if the ink is produced in the form of a gel having substantially the same consistency as ordinary printing inks. In its preferred form, the modified ink comprises a solid material acting as a penetrating agent to facilitate penetration of the paper by water, and a solvent material having a vapor pressure range of between 0.1 and 7.5 millimeters of mercury at 20 C. I have found, however, that the vapor pressure is not as critical as in the first modifications of the invention and, even though the vapor pressure of the solvent is not within the extremely narrow range preferred in the first example, the ink may still be used with considerable latitude as to type of presses and character of paper.

As penetrating agents. I may employ ordinary soap such as white castile soap and/or substantially non-oleaginous wetting agents such as the "Gardinols" and Avirols which are the sulphuric acid esters of the higher fatty alcohols and their salts such as lauryl sodium sulphate and cetyl sodium sulphate; and Igepons which are compounds of the following structural formulae:

wherein R is an alkyl radical having from twelve to eighteen carbons. and X is hydrogen or a catand similar wetting and penetrating agents of commerce. It will be noted that the Igepons are higher fatty acids or higher fatty acid amides wherein the hydrogen of a carboxyl or amino group is substituted by an ethionic acid radical. When employing the soap with another penetrating agent, the function of the soap is principally to produce the gelatinizing action. Some of the penetrating agents with certain solvents may also have the same effect. My

preferredsolventfor this character of ink is cyclohexanol, although othersolvents may also be used. This ink may have such a consistency that it may be used according to the process and employing the apparatus described in my co-pending application, in which case the soap is not used in the formula. It may also be used in the same way that ordinary printing inks are used without producing a visible mark when the paper is dry.

It is not to be understood that the ink produced in accordance with the first modification of the invention is limited only to unsized paper and that the ink made in accordance with the latter modification can be used only with fully sized paper. There is a very large amount of paper used in the printing industry which is only partially sized. An example is the so-called English finish, well-known in the printing trade.

On paper of this character, either type of ink may be used. On paper of this kind, I may use both inks together by making separate impressions, one with each ink, and so secure very novel effects which could not be obtained by the use of either ink alone. Pictures such as likenesses of, persons requiring modifications in shade can be produced with very artistic effects.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. A sympathetic ink, normally invisible when applied to dry paper of sized or unsized type but adapted to be made visible when the paper is wetted, said ink comprising a material aifecting the water permeability of the paper, and a solvent therefor having a vapor pressure between approximately 0.1 and '15 millimeters of mercury at 20 C., said material constituting on the order of 0.25% to 5% of the composition.

2. A sympathetic ink, normally invisible when applied to paper but adapted to be made visible when the paper is wetted, said ink comprising 'a moisture resisting substance, and a solvent therefor having a vapor pressure of not less than 0.1 millimeter and not more than millimeters of mercury at 0., said substance constituting on the order of 0.25% to 5% of the composition.

3. A sympathetic ink, normally invisible when applied to paper but adapted to be made visible when the paper is wetted, said ink comprising a moisture resisting substance, and the ethyl ether of ethylene glycol mono-acetate, said moisture resisting substance constituting on the order of 0.25% to 5% of the composition.

4. A sympathetic ink, normally invisible when applied to paper but adapted to be made visible when the paper is wetted, said ink comprising about one percent of a substantially colorless moisture resisting material and a solvent therefor having a vapor pressure between approximately 0.1 millimeter and 7.5 millimeters of mercury at 20 C.

5. A sympathetic ink, normally invisible when applied to paper but adapted to be made visible when the paper is wetted, said ink comprising a relatively small amount of cellulose nitrate and a solvent having a vapor pressure between approximately 0.l millimeter and 7.5 millimeters of mercury at 20 C., the cellulose nitrate constituting on. the order of 0.25% to 5% of the composition.

6. A sympathetic ink, normally invisible when applied to paper but adapted to be made visible when thepaper is wetted, said ink comprising .a material for modifying the water permeability of paper, and a solvent having a vapor pressure not greater than 7.5 millimeters of mercury at 20 C., a surface tension not greater than that of water under identical conditions, and compatible with relatively small amounts of moisture whereby the solvent is adapted to carry the material for modifying the permeability of the paper into the flberslthereof said solvent ,having a vapor pressure of notless than 0.1 millimeter of mercury at 20 C. whereby during a printing operation said ink may be permitted to dry before the paperisstacked, said material constituting on the order .of 0.25% to 5% of the composition. v v V 7. A sympathetic ink, normally invisible when applied to paper but adapted tobemade visible when .the paper is wetted, .said ink comprising a non-volatile, colorless,

consistingof cellulose esters, gums. and resins,

and a solvent having a vapor pressure of between 0.1 and'7.5 millimeters of mercury at 20 0., with a surfacetensionnot substantially greater and having compatibility than that of water with water in relatively slight amounts whereby 2 5 the solvent may carry the solute material intothe fibers .of the paper, said substance constituting onthe 0rd composition. 7 I a 8. A'sympathetic ink, normally invisible when applied. to paper but adapted to be made visible .when the paper is wetted, said ink consisting substantially of a colorless, water resisting ma? terial, asolvent therefor having a vapor pressure between approximately 0.1 .millimeter and (.5 millimeters of mercury at 20 0., and-ametallic soap in suillcient amountto cause the ink to,

take a plastic form due to the gelatinizing action of thesoap, said water; resisting material consti.-,-

tuting'on the order of 0.25% 10.5%.0! the 40 composition. 7

a. A sympathetic ink for application to bond or sized paper, said-ink being normally invisible when applied to the paper but adapted to be made visible when the paper is wetted. said ink comprising a penetrating agent and a solvent therefor having a vapor pressure between ap-" proximately 0.1 millimeter and 7.5 millimeters of mercury at 20 C., said penetrating agent consti tuting on the order 01' 0.25% to 5% of ms 5o-composition. I I a v 10. A sympatheticink for application to bond or sized paper, said ink being normally invisible.

when applied to the paper but adapted tofbe made visible when the paper is wetted, said ink water insoluble organicv substance of a film-forming class .of substances r 0.25% to -59; or the brlsing composition;

sized. paper, said ink when applied to the paper but adapted to be made i consisting substantially of soap, a penetraflng agent; and a solvent therefor, said ink being in plastic form. the penetrating agent constituting on the order of- 0.25% to 5% of the composition and the soap being present in suilicient proportions toimpart a plastic form to saidink.

. 1i. Asympathetic ink, normally invisible'hen applied to paper butadapted to be made visible.

vapor pressure. between approximately 0.1 and 7.5 millimeters of mercury at 20. C.. the cellulose acetate constituting on the order 5% of the composition.

13. A sympathetic ink for application to bond or sizedpapensaid inkbeing normally invisible when appliedv to-the paper but adapted to be made visible when the'paper is wetted, said ink asolution ;oflauryl sodium sulphate in dl-acetone, alcohol, the lauryl sodium sulphate constituting :appro'ximateiy 5% of'the 14.v A sympathetic. ink for application unbeing normally invisible visible when the paper is wetted, said ink com prising a-solution of nitrocellulose in ethyl ether of ethylene, glycol mono-acetate, the nitrocellulosejconstituting approximately between 1% and 2%'-of the composition.

15. A sympathetic ink for-application to; bond or sizedpaper, said ink being normally invisible when applied to thetpaper but adapted to be made visible when the paperis wetted. said ink comprisin'g a penetrating agent of a class con sisting of sulphuric acid esters alcohols and ethionic acid derivatives oi higher fatty acids and higher fatty acid amides: and a solvent having avapor premure of between approximately 0.1Emlllimeter and 7.5 millimeters of mercury at20 0., said penctratins esent'constituting on the order. oi'.0.35% to 5% of the composition. WALTER S. GU'I'HMARm of higher fatty 

